The present invention relates to Venetian blinds and, more specifically, to a concealed type lifting control mechanism for Venetian blind, which keeps the ends of the lift cords of the Venetian blind from sight.
A window may be provided with a Venetian blind that can be opened or closed to regulate the light, air, etc. A regular Venetian blind comprises headrail, a blind formed of a set of slats and a bottom rail and suspended from the headrail, a lifting control mechanism adapted for controlling the lifting of the blind, and a tilt control mechanism adapted for tilting the slats to regulate the light.
The lifting control mechanism comprises an external lift cord, a slat lift cord, and a lift lock. The external lift cord is suspended from the headrail of the Venetian blind at one lateral side of the slats for pulling by hand. The slat lift cord is inserted through the slats and connected between the bottom rail of the blind and one end of the external lift cord. The user can pull the external lift cord to move the slat lift cord, and to further control the elevation of the blind. Pulling the external lift cord can simultaneously move the lift lock between the locking position and the unlocking position. Therefore, the user can adjust the blind to the desired elevation by means of operating the external lift cord. Because the external lift cord is suspended from the headrail of the blind at one side of the slats, it is conveniently accessible. However, because the external lift cord is not kept out of reach of children, children may pull the external lift cord for fun. In case the external lift cord is hung on a child""s head, a fetal accident may occur. Furthermore, the external lift cord tends to be tangled with the tilt cord of the tilt control mechanism or the slats of the blind.
Taiwan Patent No. 149396 (application no. 8722193) discloses a Venetian blind lifting control mechanism, which uses a winding spring to automatically take up the external lift cord after each operation. When stopped at a particular elevation, the return force of the spring, the weight of the blind, and the friction force between the lift cord and the related elements are maintained in balance, keeping the blind positioned in the desired elevation. However, because the friction force and the spring, force vary with the wear extent of the related elements after a long use of the Venetian blind, the ends of the slats cannot be maintained in balance during elevation adjustment of the blind.
The present invention has been accomplished to provide a concealed type lifting control mechanism for Venetian blind, which is safe in use and, keeps the ends of the slats of the blind in balance during elevation adjustment of the blind.
To achieve the object of the present invention, the concealed type lifting control mechanism comprises at least two take-up reel sets, a synchronizing transmission unit and a positioning device set. Each of the two take-up reel sets comprises a lift cord take-up unit, and a spring release unit, said spring release unit providing a predetermined springy release force and linked to said lift cord take-up unit, said lift cord take-up unit being fixedly connected to the lift cords of the Venetian blind to impart a roll-up prestress to the lift cords of the Venetian blind for taking up the lift cords. The synchronizing transmission unit is coupled to the lift cord take-up units of said at least two take-up reel sets, for enabling the lift cord take-up units to be moved synchronously. The positioning device set comprises a retaining member provided between said take-up reel sets and moved between an engagement position where said retaining member engages said take-up reel sets to offset said roll-up prestress and to keep the lift cords of the Venetian blind in position, and a release position where said retaining member is disengaged from said take-up reel sets to let the lift cords of the Venetian blind being adjusted to the desired elevation.